The synthetic steroid, pregnenolone-16-alpha carbonitrile (PCN), has served for decades to probe for a postulated series of hepatic defenses activated under situations of environmental "stress". Previous research conducted to explore the full domain of genes under the control of PCN employed differential display to detect rat liver mRNA species selectively induced by PCN or by Dexamethasone(DEX). These studies revealed the induction of RT1.B (I)beta a member of the major histocompatability class II (MHC) gene family usually found only in antigen presenting cells (APC). Preliminary data obtained from rat liver or from cultured hepatocytes confirmed that amounts of RT1.B (I)beta mRNA and also of its companion gene, RT1.B (I)alpha, became readily induced within 3-6 h following DEX or PCN treatment, whereas no induction was observed in spleen (site of APC). Classical dose response experiments using glucocorticoids have always revealed inhibition of MHCII genes in immune tissues. However, gamma interferon IFNgamma is one of the most potent inducers of MHCU genes in many tissues and cells but not in hepatocytes. This unexpected induction of MHCII genes in the rat liver by glucocorticoids has opened a series of questions in terms of the possible mechanisms responsible for such effect. The concept of a set of genes coordinately controlled to maintain homeostasis in parenchymal tissues during toxic stress must now be extended to include the immune system. Due to the high similarities between rat and mice MHC-II components (91% homology in cDNA sequence) we believe that this rat liver induction phenomenon would also take place in mice. Since the MHCII mouse promoter is well known, fairly well characterized, and is very similar to humans, it would be an excellent and preferred model for studying MHCII regulation due to steroid treatment. The class II transactivator (CIITA) has been accepted as the key regulator for the transcription of MHCII genes. Three different types of promoters (I, III, and IV) have been described to regulate CIITA transcription in mice. This research is designed to determine if induction of MHC-II genes can be achieved by steroid treatment in mice as it is in rats. If this is achieved then we have an excellent model to study the mechanisms involved in MHCII induction in non-APC. We will immediately establish whether MHC II induction is dependent or independent on CIITA or whether it is through a new mechanism. We will also address which CIITA promoter is involved in this induction in the specific tissues of liver and lung. In the event that MHC II genes are refractory to steroid induction in mice we plan to continue with our rat model and fully characterize the promoter in this species in order to elucidate the mechanism associated with this phenomenon. The results of these experimentsare of utmost importance for understanding the effect of steroids on MHC regulation since many steroids such as dexamethasone are used to treat certain autoimmune diseases (characterized by over-expression of MHCII genes) at considerably high doses of up to 1000mg/day. This proposal is designed to elucidate if DEX and PCN are inducing the MHC class II genes in non-APC through its known transactivation pathway in mice and rat or through a different route independent of CIITA.